Standard T8 lamps utilizing only argon as the inert fill gas have a lower lumen efficacy, expressed as lumens per watt, as compared to argon/krypton energy efficient T8 lamps. These lower wattage T8 lamps yield reduced positive column power through addition of krypton to the fill gas. The addition of krypton reduces energy consumption in fluorescent lamps because krypton, having a higher atomic weight than argon, results in a lower wattage gradient in the positive column with lower heat conduction losses per unit length of discharge in the lamp. These lamps are known as GE Watt-Miser® lamps. However, the addition of krypton increases the peak voltage required to start the lamp, such that the lamp will not start on some ballasts, including many rapid start and programmed start ballasts. Thus, it is desirable to produce both a high efficiency lamp containing krypton capable of starting and operating on all existing ballasts so that the lamps can be rated for “Universal Operation on all ballasts”.
In order to solve the above-mentioned problem, a starting assembly is used to effect reliable starting of lower wattage fluorescent lamps with or without krypton in the fill gas. The starting assembly provides an easier path for the electrons to flow during starting of the lamp thereby reducing the peak starting voltage requirement of the lamp.
One conventional starting aid consists of a conductive metal strip attached to the outside of the lamp. In a typical embodiment, the metal strip on the outside of a 1.5-inch (120 mm) circumference T12 fluorescent lamp is approximately ¼ inch (6 mm) wide and extends the length of the lamp. This method has several disadvantages. The major disadvantage is that the metal strip starting aid covers a relatively large percentage of the subtended circumference of the lamp envelope of approximately 5%. Since the metal strip extends nearly the entire length of the lamp envelope, it thereby covers approximately 5% of the surface area of the lamp envelope and therefore it absorbs or reflects approximately 5% of the light emitted by the lamp. Even though some of the light reflected by the metal strip is redistributed inside the lamp and is re-emitted, nonetheless the total emission of the lamp is reduced by a substantial amount of more than 1% due to absorption of light by the strip and inefficiencies inside the lamp. A second disadvantage of the wide metal strip is that it is visible to the customer at distances of four feet or more. Another disadvantage is that the metal strip is typically manually attached to the lamp with an adhesive and an insulating cover to prevent electric shock to the installer. This manual manufacturing process significantly increases the cost of manufacturing.
Another conventional starting aid consists of applying a conductive coating, such as tin-oxide, over the entire inside surface of the light transmissive envelope. Similar to the metal strip above, a major disadvantage to this method is that it covers 100% of the total surface area of the light transmissive envelope of the lamp, and the tin oxide coating absorbs some of the light emitted by the lamp. Thus, the tin-oxide also typically blocks over 1% of the lumens generated by the lamp. Another disadvantage is that the tin oxide coating creates potential safety and lamp breakage concerns during the manufacturing process. Additionally, from an environmental perspective, a corrosive agent is required during the coating process. Still yet another disadvantage to this method is that it doesn't optimally perform on T12 lamps utilizing an electronic ballast.
Yet another conventional starting aid is using the metal lumiaire into which the lamp is mounted as the starting aid. However, as will be seen below the starting voltage required to start the lamp increases as the distance between the lamp and the starting aid increases. Thus, the greater the distance between the lamp and the starting aid the less efficient will be the starting aid. Further, this invention relaxes the requirements on the distance between the lamp and the metal luminaire, and even enables the use of non-conducting (e.g. plastic) luminaires, or even the elimination of the luminaire, while still providing excellent starting of the lamp.
To overcome the above-mentioned problem and disadvantages, the present invention claims that lower wattage fluorescent lamps can be made to start on all ballasts by adding a starting assembly to the lamp comprising an array of conductive paths to either the inside or outside surface of the lamp or by imbedding the conductive paths inside the lamp envelope.